OSPF Areas: Normal, Stub, and NSSA

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Questions and Answers

Which OSPF area type receives all LSA types, including Type 1, 2, 3, 4, and 5?

Normal Area (correct)

Not-So-Stubby Area (NSSA)

All OSPF areas

Stub Area

Which OSPF area type is ideal for areas where external connectivity is limited?

Stub Area (correct)

Any OSPF area

Normal Area

Not-So-Stubby Area (NSSA)

What is a characteristic of Area Border Routers (ABRs) in Normal Areas?

They do not receive external routes.

They interface to other areas and can import/export routes. (correct)

They summarize external routes and inject a default route.

They receive only Type 1 LSAs.

What is a disadvantage of using Normal Areas?

They have higher memory and CPU usage due to larger routing and LSA databases. Signup and view all the answers

What is an advantage of using Stub Areas?

They have lower CPU and memory requirements. Signup and view all the answers

Which OSPF area type is typically used for core and main areas?

Normal Area Signup and view all the answers

What is a characteristic of Stub Areas?

They receive only Type 1, 2, and 3 LSAs. Signup and view all the answers

What is a disadvantage of using Stub Areas?

They may result in suboptimal routing due to limited external visibility. Signup and view all the answers

How do ABRs behave in Stub Areas?

They summarize external routes and inject a default route. Signup and view all the answers

What is a characteristic of Normal Areas in terms of routing information?

They have complete routing information, including external routes. Signup and view all the answers

What type of LSA is converted to Type 5 LSA by the ABR when advertised outside the NSSA?

Type 7 LSA Signup and view all the answers

Which type of OSPF area is suitable for core networks requiring full routing information, including external routes?

Normal Areas Signup and view all the answers

What is the main advantage of using NSSA over normal areas?

Increased flexibility in introducing external routes Signup and view all the answers

Which type of OSPF area is best suited for peripheral networks with limited external connectivity?

Stub Areas Signup and view all the answers

What is a disadvantage of using NSSA compared to stub areas?

Higher memory and CPU usage Signup and view all the answers

Which type of LSA is not received by an NSSA?

Type 5 LSA Signup and view all the answers

What is the primary function of an ABR in an NSSA?

Converting Type 7 LSAs to Type 5 LSAs Signup and view all the answers

What is a key trade-off in choosing between NSSA and normal areas?

Routing complexity versus resource constraints Signup and view all the answers

What is the primary advantage of using normal areas over NSSA?

Full routing information, including external routes Signup and view all the answers

Which type of OSPF area provides a compromise between stub and normal areas?

NSSA Signup and view all the answers

Study Notes

OSPF Area Types

OSPF uses different area types to optimize routing and manage large-scale networks: Normal Areas, Stub Areas, and Not-So-Stubby Areas (NSSA).

Normal Areas

Supports all OSPF route types, including intra-area, inter-area, and external routes (Type 5 LSAs).
Receives all LSA types (Type 1, 2, 3, 4, 5).
Interfaces with other areas and can import/export routes to/from other OSPF areas and external networks.
Typically used for core and main areas where full routing information is needed.
Pros: full visibility of the entire OSPF network, complete routing information for optimal path selection.
Cons: higher memory and CPU usage, more complex to manage.

Stub Areas

Does not accept external routes (Type 5 LSAs), instead, a default route is injected by the ABR.
Receives only Type 1, 2, and 3 LSAs.
Summarize external routes and inject a default route into the stub area.
Ideal for areas where external connectivity is limited and a simple routing structure is required.
Pros: reduced LSA database size, lower CPU and memory requirements, simplified configuration and maintenance.
Cons: limited visibility of external networks, may result in suboptimal routing.

Not-So-Stubby Areas (NSSA)

Allows limited external routes (Type 7 LSAs) that can be converted to Type 5 LSAs by the ABR.
Receives Type 1, 2, 3, and 7 LSAs, but not Type 5 LSAs.
Convert Type 7 LSAs to Type 5 LSAs for external areas.
Useful for areas that need to inject external routes without fully supporting all external LSAs.
Pros: flexibility to introduce external routes into a semi-stub area, reduced overhead compared to normal areas.
Cons: complexity in managing and converting Type 7 to Type 5 LSAs, may still have higher memory and CPU usage compared to stub areas.

Choosing the Right OSPF Area

Depends on specific network requirements, including need for external routing information, resource constraints, and desired level of routing complexity.

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Description

This quiz compares and contrasts the three primary types of areas in OSPF: Normal Areas, Stub Areas, and Not-So-Stubby Areas (NSSA). Understand the characteristics and differences between them.